Ductile thorium and method of making the same



DUCTILE THORIUMAND METHOD OF MAKING THE SAME Filed June 5, 1924 F|G 2g-5- 30 7 724 F G-I r 4 II"- Z I 1 /z INVENTOR JOHN W. MARDEN w BzARvLaR E TscHLs/z III f zz/ ATTORNEY Y Patented July 14, 1931 UNITED STATESPATENT OFFICE JOHN WESLEY MARD'EN AND HARVEY CLAYTON BENTSCHLER, OF.EASTORANGE, NEW JERSEY, ASSIGNORS T WESTINGHOUSE LAMP COMPANY, A CORPORATIONOF PENNSYLVANIA DUCTILE THORIUM AND METHOD OF MAKING THE SAMEApplication filed June 5,

This application is a continuation of our prior applications referred tomore fully hereinafter.

This invention relates to the production of the more refractory metalssuch as uranium,

More particularly the invention pertains to the production of suchmetals in a substantially pure, coherent, homogeneous and ductile form,

An object of the invention is to provide a method for the production ofsuch metals or alloys thereof with one another or with other metals inthe powder form and in such a manner that their particle size andfreedom from deleterious substances affecting their malleability andductility may be readily and effectively controlled,

It is another object to provide a process for the production of suchmetals or alloys thereof with one another or with other metals in acoherent and homogeneous form.

so their workability or ductility.

It is a further object to provide a commercial process for theproduction of the more refractory metals, such as those mentioned, in acoherent, homogeneous and ductile form.

It is a still further object to produce coherent, homogeneous, ductilethorium, and the like, that may be readily worked into wire, sheet, discor other desirable form.

It is yet another object to provide an improved apparatus for carryingout the invention.

Additional objects will become apparent upon reading the description,claims and drawings, in which Fig. 1 is a view in vertical section of abomb in which a part of our process is carried out; and

Figs. 2 and 3 are diagrammatic views of 1924. Serial No. 717,940.

the furnaces for heat-treating the metals and the control circuitstherefor.

A number of methods have been proposed heretofore for the production ofthe metals above mentioned but to our knowledge, no one has succeeded inproducing such metals in a homogeneous, coherent and ductile state. Manyof these metals are extremely active when in the finely divided stateand readily combine with oxygen, nitrogen, and other elements and forthat reason, their con:

version into the fused or solid, coherent metallic state is attendedwith the greatest difficulty. The powders of such metals coated with anoxide, for example, cannot be formed into a workable homogeneous bodyfor the reason the oxide prevents the metals from coalescing.

It has been suggested to prepare the powders of the metals of thecharacter specified by the reduction of their oxides by means of calciumunder suitable conditions, but no particular attempt was made to controlthe purity or size of particles of the metal produced, nor was itpossible to cause the metallic powders prepared by the calcium reductionprocess. to coalesce or fuse into coherent, homogeneous and ductilemetallic bodies. As early as 1904, Huppertz (Chemisches Centralblatt(1904) vol. 1, page 1383) published a method for the production of therefractory metal powders, such as of titanium and the like, by action ofcalcium vapor on titanium oxide or other oxides when heated in anelectric furnace.

A more extensive investigation on the cal cium method of reduction ofrefractory oxides was published by Burger in 1907. (Dissertation atBasel, 1907.) See also Gmelin Kraut Handbuch der Anorganische Chemie.Vol. III, part 1, page 1207. Kuzel and Wedekind (Br. Patent 23,215 Oct.11, 1909; U. S. Patent 1,088,909, March 3, 1914) have patented thismethod for the production of many of the metal powders listed aboveusing calcium metal for effecting the reduction. These methods, however,are not satisfactory for preparing metallic powders from Which Coherent,homogeneous,

ductile metallic bodies may be produced because of contamination, etc.

A method of converting tungsten powder to the coherent metallic state iswell known but such method is dependent upon a special process forobtaining the metal powder and also upon a complicated and long drawnout series of mechanical operations before it is had in satisfactoryductile form. This method of preparing ductile tungsten is whollyunsatisfactory for the production of the metals heretofore specified,because of their greater chemical activity and also because their oxidesare not reducible by hydrogen.

The present invention, therefore, provides a process for the productionof the metals of the character above noted in coherent, homogeneous andductile form in a practical manner, from stable compounds which areavailable on the market in relatively large quantities.

In practicing the invention we begin with a compound of the metal,purify it, if necessary, reduce the same and subsequently treat themetal thus secured by heat and by other means to obtain a coherent,homogeneous, ductile metal product.

In an application by John W. Marden ct al., Serial No. 618,544, filedFebruary 12, 1923, entitled Method of preparing refractory metals andassigned to the assignee of the present application, a process for thereduction of refractory metal compounds to obtain the metallic powderhas been described, and in practicing the present invention, we havefound it desirable to follow the calcium-calcium chloride reductionprocess set forth therein with certain advantageous modifications andvariations which will be described. more fully hereinafter. This processmay be termed the first step in our process. For what we may term thesecond step of our process; namely, sintering and treating to thecoherent and homogeneous metal form, we prefer to follow, with certainadvantageous modifications, the process substantially as set forth inour application, Serial No. 432.325, filed December 21, 1920, entitledSintering and fusing of metal powders into coherent metals and assignedto the assignee of the present application, the present applicationbeing a continuation-in-part thereof and we may utilize, for practicingsuch heat-treatment, the furnace described in the patent to Harvey C.Rentschler, No. 1,480,301, issued January 8, 192-1, entitled Furnacesand assigned to the assignee of the present application. We may employfor some purposes the furnace described in ourcopending application,Serial No; 488,230, filed July 28, 1921, entitled Furnaces and alsoassigned to the assignee of the present application. A third step may bereferred to as fabricating the metal.

We have found that by a combination of the processes set forth in thecopending applications, noted supra, when practiced in accordance withthe modifications hereinafter set forth, we are able to obtain arefractory metal of the character previously referred to in homogeneous,coherent and ductile form which, to our knowledge has not been doneheretofore. In other Words, we reduce compounds of the metals to obtainmetallic pmvders free from deleterious substances affecting themalleability of the metals, thereafter heat-treating the metal particlesto cause them to coalesce into a coherent, homogeneous, ductile mass andthereafter fabricatev such metal into ucful forms, such as wire, sheet,plate and the like.

More specifically our present invention contemplates the reduction ofcompounds of the metals under consideration to obtain the metallicpowders thereof free from contamination. This reduction is effected in abomb by employing a suitable flux such as calcium chloride and, areducing agent such as calcium by the process hereinafter fullydescribed. The purity of the metallic oxide employed is a specialfeature of the inven tion as will be appreciated later. Upon obtainingthe pure powder of a given metal it is subjected to a sintering andheat-treatment under non-oxidizing conditions during or between saidheat-treatments. As a result of these treatments a bar or slug of themetal is produced which may be fabricated or worked into any desiredform, the resultant product possessing ductility, malleability, etc.These several steps for the sake of clearance are taken up and describedin detail below.

However, in order to obtain themetals in a homogeneous, coherent, andductile state, it is necessary that the chemical materials utilized ineffecting the preparation of the metallic powders be prepared withspecial care, and for this purpose we provide special methods for theproduction of such materials free from deleterious substances thatadversely affect the workability of the resultant metals. Therefore,before proceeding with the detailed description of the main processcontemplated herein, we will first set forth the preparation of thechemical materials of the desired purity together with a description ofthe bomb in which the chemical reduction of the metallic oxides iseffected.

Preparation of calcz'mn chloride We prefer to employ as a fluxing agenta halide of an alkaline earth metal such as calcium chloride, but othersuitable metal halides may be employed for this purpose.

The calcium chloride should be in a very pure condition and care shouldbe exerclsed to see that any chemical impurities WlllClLll) may containare removed. Generally we have found that certain grades of calciumchloride available on the market are sufiiciently clean so that theyneed only be heated to about 450 C. to thoroughly dry them. The dryingof the calcium chloride may be performed in any suitable form of heaterwhich will not introduce impurities and which is capable of control sothat the temperature for drying may be maintained at about 450 C. for asufiicient period of time. The calcium chloride after drying, may bepulverized to pass a 40 or 60 mesh sieve and maintained in the drycondition until used. It should be stated here, that the rate ofreaction may be effectively controlled by increasing or decreasing theamount of calcium chloride or other fluxing material and the amount ofalkaline earth metal reducing agent. By thus controlling the rate ofreaction and varying the temperature of the bomb, the size of the metalparticles may be satisfactorily governed, as will more particularly.appear here'nafter.

The calcium chlo ide is added principally for the following purposes:first, to act as a flux to form a more or less fiuid medium in which thereaction takes place; second, to take up the calcium oxide which is oneof the products of reaction with the formation of oxy-compounds, toremove it from the zone of reaction and to allow the reaction to go tocompletion; third, to permit the thorium metal, which is heavy, tosettle to the bottom and thus afford an effectual seal against oxidizinginfluences, and; fourth, dependent upon its proportion, to increase ordecrease the reaction rate.

Preparation of the calcium We find it desirable in practicing ourprocess to employ a reducing agent, such as calcium, which is free fromdeleterious substances.

The calcium used for our process maybe made from calcium chloride, suchas the above stated, by the electrolytic process, and for our purpose,we have used calcium which has shown on analysis not more than .02 or.03 of 1% iron and proportionately low impurities of other sorts. If thecalcium chloride used in the production of calcium has been carefullyprepared, the resultant product will be proportionately purer. Inpractice, we have found it best to discard the first piece of calciummade from a fresh electrolytic bath, since iron and other impuritiesappear to concentrate therein. The calcium thus prepared is maintainedin an inert environment until ready for use. When ready for use, thesurface coatings of oxide and calcium chloride are removed deteriorationin the atmosphere, the calcium cuttings are, immediately mixed with themetal oxide and the fluxing agent and loaded into the bomb.

Preparation of the mmllz'c o-aa'de As hereinbefore mentioned, we preferto produce thorium metal powder from thorium oxide and for that purpose,the latter should be prepared with special care. Thorium nitrate may beignited in sucha manner, that thorium oxide produced therefrom is coarseand heavy, that all nitrate-- is destroyed, and that no impurities areintroduced. Great care must also be taken-- to ignite the thoriumnitrate at such a tem-' perature, that the thorium oxide when formedwill not be heated to too high tem' peratures for this will prevent themost satisfactory reduction. In explanation at this point, it may bestated that results seem to indicate that thorium oxide heated tocertain temperatures will be more readily reducible, than if it beheated to higher temperatures, which makes it quite diflicult to reduce.In order to get pure thorium oxide and to avoid the introduction of anyimpurities, such as silica, we may ignite the thorium nitrate verygently in a porcelain dish of the wide type in an electric furnace, butnot over the open gas flame where there is a possibility of introducingcarbon or other impurities.

The first gentle ignition of the nitrate to about 400 to 500 (1, causesthe thorium nitrate to puff up and form a voluminous mass whichafterwards sinks down, gradually becontlng more compact. If the heatingbe continued in the porcelain dish to too high a temperature, the thoriaseems to absorb or take up a small amount of silica which is mostundesirable and for this reason, after the pulling is over, themasssubstantially settled and the nitrate practically destroyed, the powder.is placed in relatively small portions in platinum crucibles and theignition continued to aboutSOOff or 850 C. in the electric furnace todestroy- The oxide thus prepared tion to many metals, including thosehereinbefore mentioned, with perhaps slight modi-' The bomb Beforeproceeding with the detailed description of our process, we will firstdescribe the special bomb in which we prefer to practice the chemicalreaction, ref

erence being had to Fig. 1 of the accompanying drawings for the purpose.

The bomb construction differs from that set forth in application, SerialNo. 618,544 referred to, in that a plug 2 having a taper 4, i. e., ataper of slight angularity, is adapted to fit Within a similarly taperedopening in the cylindrical bomb 6 and may be forced therein to a tightfit by means of a projection 8 adapted to be eompressively engaged by ascrew cap 10 which is secured to the bomb by means of screw threads 12.The cap 10 is also provided with a projection 14, similar to theprojection 8 so that each may be engaged by a wrench or other tool forturning them. After a charge has been inserted into the bomb, the plug 2is put in place and may be gently turned to insure intimate contactbetween its tapered sides and the tapered seat formed in the bomb wall.The cap 10 is then screwed down upon the bomb until it engages theprojection 8 with the desired degree of compression. In opening thebomb, this process is reversed,-the projection 8 providing means to gripthe plug 2 for its removal.

The taper 4 may be of any desired angle but since a long taper makes theplug difficult of removal and a short taper does not provide the wedgingaction necessary to secure a tight joint, weprefer a compromise betweenthe two as shown. The plug and its tapered seat 4 should both becarefully ground to provide a tight fit for it is necessary that ahermetic seal be maintained. The bomb may warp to a slight extent afterit is first used, in which case the stopper or plug should be regroundand reseated. We have found through experiment that the stopper rarelyneeds further working after it has been reground once or twice.

The bomb may be made of iron or steel or of an other metal orcomposition that will withstand the temperatures and pressure incidentto the reaction within and that will not contaminate the product. Thethreads of the cap of the bomb may be painted with a paste made offiuffy magnesium oxide and water which serves two purposes; to fill thejoint to maintain it airtight and to keep the iron threads from stickingafter high temperature treatment.

As it is of prime importance that the metal produced in the bomb bewholly uncontaminated, we have found it preferable to make one run inthe bomb before it is used for the production of the best powder. Thismay be because the iron of the bomb contains small amounts of carbon,silica and other impurities which are impossible to remove in any way,other than to soak them up during the heat-treatment of the metalpowders which it is desired to make.

It is extremely necessary for successful results, that the bomb becleaned thoroughly of rust and other deleterious substances which mayaffect the purity of the product. For rust and the usual impuritieswhich collect within the bomb, we have found that hydrochloric acid andwater in equal proportions with perhaps a small amount of acetic acid isquite'effective for the purpose. Formic acid or almost any other organicacid may be used in place of the acetic acid.

Before a run is made and after the stopper has been ground into place,the acid mixture is poured into the bomb up to the edge of the groundjoint, care being exercised to avoid wetting the ground joint with theacid. If the rough layer of oxide is thin, a few minutes will sufiice togive a clean white iron surface, whereupon the acid is quickly pouredout and the bomb thoroughly washed with water to remove as much of theacid as is possible. The drying may be completed by rinsing withalcohol, etc., wiping out with a clean dry cloth and finished by blowingclean air over the surface.

As hereinbefore stated, the bomb may be provided with an insulatinglining (not shown) of calcium oxide, as disclosed in application, SerialNo. 618,544 previously referred to, an oxide of other alkaline earthmetals, magnesium, alumina, or any material that will not deleteriouslyaffect the product, or it may be lined with a metal such as platinum,tungsten and the like, if desired. In some instances, such as thatselected for description herein, the lining is unnecessary, but if alining be used it may be of the thickness set forth in application,Serial No. 618,544. However, the thickness may be varied over wideranges.

In the foregoing description we have been concerned with the preparationof the chemical materials employed in practicing our main process forthe production of the metals under consideration. This process dividesitself into three steps or stages which will now be described.

Preparation of the metallic powder The ingredients for filling the bombhaving been made ready as hereinbefore specifically pointed out, we findit preferable to use one part of the metal oxide with one part ofcalcium chloride and three quarters and to finally weigh out thecalcium. The

dry pulverized calcium chloride is mixed with the coarse and heavythorlum oxide,

and the pure metallic calcium cuttings, with the exception of a smallportion added and the mixture agitated to thoroughly intermix theparticles of the ingredients. We prefer to do the mixing within astoppered bottle by thoroughly shaking it, since calcium chloride andcalcium readily absorb moisture and oxygen from the atmosphere when notunder seal.

While the mixture thus made be compacted into cakes and placed withinthe lined bomb as set forth in said application, Serial No. 6185M, weprefer to quickly pour it from the mixing container into an unlinedbomb, press it down gently, place the remaining portion of calciumcuttings on top of the charge, insert the wedgeshaped stopper in placeand turn it gently to properly seat it.

The screw cap is then placed upon the bomb and turned down' until thedesired degree of compression of the stopper has been attained. While wemay prefer to slightly compact or compress the charge within the bomb,it is generally unnecessary to do so if an excess of calcium be used toclean-up the air.

The bomb is now placed in an electric furnace, a pyrometer inserted fortemperature readings, the temperature increased to about 950 C., andmaintained constant for such period of time as may be necessary to allowthe bomb to obtain the same temperature throughout, as that of thefurnace.

Upon the completion of the heating, the bomb is lifted out of thefurnace While bright red hot and allowed to stand in the air for a fewminutes to cool, whereupon it may berapidly cooled in any suitable man--ner such as by cold running water.

It has been found by experience that the bomb should be thoroughlycooled before opening it. A bomb originally containing about one quarterof a pound of metal oxide may require about an hour of this treatmentfor thorough cooling and no attempt should be made to open the bombuntil it is quite cold to the hand, because of the chemical activity ofboth thorium and calcium when slightly warm or hot. The screw cap may beremoved in any suitable manner and the top around the tapered plugthoroughly cleaned. The charge, which consists of a compact mass ofcalcium chloride, calcium oxlde, thorium and excess calcium, may beremoved from the bomb in any suitable manner as'by chiseling. 1

Before cutting out the charge, filtered water is prepared for itsdisintegration and for this purpose, we prepare about 80 liters perpound of thorium oxide used for the first washing and disintegration.This great volume of water is necessary in order to maintain the mixturecool to prevent thorium oxidation.

The fine material, as it is cut from the charge within the bomb, isadded in small portlons at a time into a vessel containing the filteredor distilled water while continuously and vi orously stirring it toprevent the particles from settling in one place and heating.

lVhen the charge has been cut out by the chisel, drills or other means,as far as it is practical to do so, the bomb itself may be set in a dishof cold running water and while kept cool, filtered water run within todisintegrate the remaining material clinging to the sides and bottom ofthe bomb. The material so obtained may be poured into the large bulk ofthe solution.

After gas has ceased to be evolved, stirring is discontinued, theinsoluble material permitted to settle, and the liquid poured orsiphoned off. A second portion of distilled water in the ratio specifiedabove is added and the mixture again stirred for five or tenminutes,whereupon the residue is allowed to remain and the supernatantliquid again poured away. This should be done several times until theliquid above the insoluble material has become clear or is slightlydark, due to the suspension of a small amount of extremely finelydivided thorium. This may be safely poured away since the amount ofthorium lost is small and it is desirable to remove any exceedingly finethorium powder.

After the final Washing with water, two or more liters of filtered waterper quarter pound of thorium oxide may be added to the residue and themixture stirred with considerable violence while from 250 to 300 cc. ofconcentrated nitric acid is slowly added. This will give a solution ofabout 1 part HNO to 8 parts H O. It will be noticed that a copiusevolution of gas takes place, but if the process has been carefullyfollowed, only a slight indication of the presence of carbides in thecalcium or thorium oxide by the evolution of acetylene will be observed.Five minutes of intensive washing with the acid may be given and there-This acid washing may be repeated about,

three times depending upon the continued loo evolution of gases. If, forexample, any odor of hydrogen sulphide remains upon a third. acidwashing, the acid treatment should be repeated at least twice more.

Upon the completion of the acid washing,

the charge is washed two or more times with 20 liter portions offiltered water to remove the acid, the metal powder is filtered upon aBuchner funnel, washed with alcohol and ether and sucked as dry aspossible with an aspirator. The powder while still somewhat wet, isplaced upon a 60 mesh sleve and as it dries, is brushed through into atube or the like so that it may be connected to a vacuum pump to removethe remaining alcohol, ether and any moisture remaining and to obtain itin as clean and as dry a condition as possible.

The powders produced consist of bright particles with clean surfaces asseen under the microscope but upon exposure to the atmosphere theirsurfaces become dimmed over or dull with an oxide coating. The powdersthus prepared show by actual chemical analysis to be substantially freefrom oxide or other deleterious substances which would prevent thesubsequent heattreatment hereinafter specified from converting thepowder into a coherent, homogeneous and ductile body or mass.

Sz'ntem'n'g and heat-treatment The metal powder whether produced by theprocess outlined above or by any other process which will produce a purepowder susceptible of being pressed into slugs or buttons of the desiredshape and sintered into a ductile or malleable body, is now ready forthe sintering and treating process.

As above, we shall consider thorium for illustrative purposes and willdescribe the process specifically applicable to that metal, although itwill be understood that with slight modifications, according to thepeculiarities of the material, it may be applied to the production ofother metals. The button or slug having been formed by suitable pressureand without the addition of any binding material, is placed within thefur nace for sintering and heat-treatment. This furnace-may be either ofthe type described in our aforesaid copending application, Serial N 0.488,230, or that described in Patent No. 1,480,301. In either case, thehighest vacuum or a completely inert atmosphere must be obtained andmaintained from the beginning to the completion of the heattreatingprocess.

In Figs. 2 and 3 of the drawings, we have shown two types of furnaces,together with the circuits for their operation.

Referring to Fig. 2 of the drawings, a vitreous envelope 16, containingan induction coil 18 hermetically sealed therein, may be connected to anexhaust line 20 by means of connection 22. Connections from anelectrical source 24 comprise an adjustable rheostat or a variableinductance 26, a step-up transformer comprising primary and secondarywindings 28 and 30, respectively, air choke coils 32 to eliminate highfrequency surges fromharming the transforl'ner, a condenser 34 and abattery of mercury spark gaps 36 arranged in parallel so that one ormore may be used as desired. The charge to be treated may be placedwithin the coil 18 and supported in position upon or within a crucible19 or disk of thoria or other desirable high melting point materialwhich may be supported by a wire 19'. This brieflydescribes the furnacetogether with the circuit arrangement, partly described and claimed insaid Patent 1,480,301.

As shown in Fig. 3, the furnace described and claimed in saidapplication, Serial No. 488.230, comprises a vitreous envelope 38 withinwhich electrodes 40 and 42 are hermetically scaled, the electrode 42making contact with a pool of mercury 44 which serves to maintaincontinuous contact with the metal slug 46 through the clip 48 se curedto the lower end of the slug, the upper end of which is clamped to theelectrode 40. The circuit for this furnace comprises a step-downtransformer 50 and a variable resistance or reactance 52 for the primarythereof.

For the purpose of observing the degree of vacuum attained or existingwithin the furnaces 16 or 38, we prefer to use spectrum tubes,designated 54 and 56 for the induction furnace 16 and the contactfurnace 38, re spectively. These tubes are of the ordinary dischargetype having electrodes about four inches apart with a capillary tube ofabout one-eighth inch inside bore connecting the bulbous portions. Thesetubes are operated by having about 3000 volts from small transformers 58and 60, connected to a suitable source not shown, impressed between theelectrodes. -The use and value of these spectrum tubes for determiningthe degree of vacuum within the furnaces will be clearer as thedescription proceeds.

The spectrum tubes may be replaced or used in conjunction with McLeodgauges (not shown) but we prefer to use the former. Instead of usingeither the spectrum tube or gauge for the induction furnace, a discharge between turns of the high frequency. coil or to the leading-inwires may serve as an indication that gases are being evolved toorapidly or, if the discharge does not take place, it may be consideredas an indication that the gases are being liberated in a satis' factoryand not too rapid manner.

In preparing metal for its manufacture into sheet or the like form, wemay prefer to use the furnace 16 and for such purpose, the slug orbutton is mounted within a crucible or upon a plate of thoria 19 orother suitable material that is positioned substantially centrallywithin the high frequency coil. In this case, of course, the heating isdone by high frequency induction, while the vacuum pumps are operatingto remove any gases given off by the metal during treatment.

The heating schedule is carried out slowly at first, in order to causethe evolution of gases from the wall of the furnace and from within thebutton or slug and thereafter the heating current is gradually raised-atsuch a. rate that the gases and vapors are expelled from the metal undertreatment without fracturing the specimen or causing chemical reactionof the gases therewith. A suitable vacuum is maintained to avoidobjectionable arcing between the turns of the high frequency coil of thefurnace.

Upon heating the mass, gas may be evolved from the metal undertreatment, in this case from the thorium, and the presence of anobjectionable quantity may be indicated by the character of dischargetaking place in the spectrum tube. The absence of any discharge may betaken as an indication that the gases are not being too rapidly libertyand will not deleteriously affect the metal undergoing treatment.

Should it appear from the spectrum tube or from other sources that thegases are being given off too rapidly, it is advisable to diminish thecurrent through the primary until the evolution is reduced to asatisfactory rate. No prediction can be made as to what rate ofevolution of gas should be maintained, since many variable factors comeunder consideration in this connection and the best that can be said isthat experience and experimentation must be relied on in each separateinstance.

Upon continued treatment, the metallic mass becomes sintered along theedge first, becomes a better conductor and causes further sinteringprogressively to the interior, until all the powder becomes coherent andhomogeneous. The degree of heating determines the uniformity of thesintered metal and generally the longer and hotter the slug or button isheated, the more dense and coherent it becomes. The temperature of thethorium being treated should be increased until it is raised to near itsmelting point and maintained thereat until such time as all particlesthereof sinter together or coalesce into a homogeneous coherent form.

e have also discovered that thorium metal may be melted in or on thoriaor other suitable containers or supports and that the fused metal may beused for extensive cold working. The purity .of the product is indicatedby the definiteness of its melting point.

In cases where it is desired to manufacture a long slug of metal fromwhich Wire, sheet, plate or the like may be fabricated, we prefer toemploy the furnace. described and illustrated in our copendingapplication, Serial No. 488,230, previously referred to, and hereinaftertermed the contactfurnace.

Bars of thorium, for example, in the coherent, ductile state, may beprepared as follows. The pure metal powder is formed into compact slugsby subjecting the powder to pressure within a separable mold. Thequantity of powder required for each molding operation is carefullyweighed, such quantity being determined by such factors as size andshape of the compressed slug. The weighted powder is placed within themold in such a manner, as to obtain a uniform distribution within thesame and is then subjected to a pressure transversely to thelongitudinal axis of the mold or the slug, of such a degree as tocompactthe powder so that the slug which is formed thereby may bereadily handled and clamped within the contact furnace.

In removing the slugs from the mold, care should be exercised to seethat they are not cracked and we have found that cracking may be avoidedby first withdrawing the end sections of the mold, thus permitting thecompressed powder to expand along the longitudinal axis of the slug.

It was found unnecessary to previously sinter these slugs or bars in anatmosphere of hydrogen, as is the case with tungsten and molybdenum,because the pressed slugs are very rigid and may be easily handle-dwithout danger of fracture.

Oneend of the slug is then secured to the upper clamp within thefurnace, a lower clamp being fastened to the lower end of the slug, thelength of the clamp being such as to maintain contact with the mercuryelectrode in the bottom of the furnace during the heat-treatment of theslug.

After the furnace has been carefully sealed, a very high vacuum isproduced within the furnace and thereafter a low current is passedthrough the slug. This current is gradually raised at such a rate, thata good vacuum may be maintained throughout the heat-treatment. The sectrum tube may be employed to indicate t e degree of vacuum. At first,the slug is not as good a conductor of the current owing to the presenceof gases therein and during the early stages, it may' be found necessaryto utilize a higher Voltage in order to pass the low current. Aftersubstantially all the gases have been removed, the current may beincreased to approximately 85% of the current required to fuse the barand this current maintained for approximately 12 to 15 minutes until thebar is in a thoroughly sintered condition. Vith a H square bar and 3 inlength, it was found that at about 21 amp. of current in the primary ofthe transformer 50, having a ratio of about 20 to 1, that the bars wouldmelt olf. After determining this temperature, the value of the heatingcurrent was determined to be from 20 to 90 amp. in the primary of thetransl'm'mcr. If the bar is of larger size, for example A in diameter,the heating current is approximately 550 amp.

In treating the bar, care should be exercised in maintaining control ofthe treating current, for the reason that during the dcgasifying of thebar, some times the resistance of the bar may suddenly decrease, whichobviously produces a rush of current through the bar which results inthe fusion of the metal.

After the bar has been thoroughly treated to sinter or weld theparticles of metal into a coherent mass, the current may be turned off.The bar should be permitted to cool within the furnace and should not beremoved therefrom until it is quite cool, otherwise it will be subjectto oxidation.

From bars prepared in accordance with the preceding processes, we havefabricated very fine thorium wire which is quite ductile when cold.

It is not necessary to start with the pow der of the metal for theprocess may be prac ticed by employing compounds decomposable at hightemperatures. For instance, thorium hydride may be readily decomposed byhigh temperature treatment in a vacuum.

Although the invention as herein described relates to the production ofa homogeneous, coherent metal, it may be well adapted to the productionof alloys containing several metals, as will be readily perceived. Inpreparing such alloys, we may utilize a mixture of metal powders of twoor more of the more refractory or rare metals and sinter the mixture ineither of the furnaces in accordance with the process described supra;or we may mix a rare metal powder with one or more of the more commonmetal powders and sinter or fuse the same to form an alloy.

We may also produce alloys from the compounds of rare or other metals asfrom hydrides, or the like. 7

Fabrication splinters by occasionally heat-treating at low temperatures,for substantially low temperatures, during mechanical working. We haveformed the metal by cold-working into wire electrodes and other usefulshapes and articles, admirably adaptable for a. wide variety ofpurposes.

A few specific instances of preparation into useful articles will bedescribed. In making disc-targets for X-ray tubes, we have pressed themetal powder into cakes or buttons about f thick and about an inch and ahalf in diameter, and have followed the process hereinbefore set forthfor the high frequency induction furnace, treating the button forseveral minutes at a temperature just below the melting point of themetal and rolling, when cold, to the thickness desired. lVe have madethorium discs for this purpose with a heat-treatment of seven minutesafter the gases were removed. After thorough cooling, we crossrolled thebutton with flat rolls to a thickness of inch. The edges were trimmedoft to make a round disc which was used very eil'ectively in an X-raytube.

In mainlfacturing thorium wire, we treated the slugs as has beenpreviously described and in the best vacuum attainable and thereaftercut the bars into 1 inch lengths for convenience. They were then trimmeddown to 1; inch round rods and placed inside inch (outside diameter)iron tubes so that the thorium rod tightly fitted within them. Coldrolled steel was not as satisfactory for our purpose as very soft andpure Norway iron (such as that used in welding).

Norway iron of this character can be rolled and drawn without splittingand does not develop cracks on long continued working as doescold-rolled steel. e were able to roll down the composite bars to about30 mils diameter with grooved rolls and thereafter draw the wire down toabout 7 mils with dies. This yielded pure and ductile thorium wire ofabout 1 to 3 mils diameter after the iron was removed with a warm, 1 to8 or 1 to 6, nitric acid solution. The wire thus formed is of uniformdiameter, strong and is readily adapted for. filaments for lamps andother purposes.

These fabrications have indicated the very great ductility of thoriummetal as it was susceptible of extensive cold working. It has been shownupon chemical analysis and by microphotographs, that the thorium metalwe have obtained is substantially pure. It has also been found that themelting point of thorium is about 2100 K., its density or specificgravity 11.3, its specific resistance 18 to 20 10' ohm ems. at roomtemperature and its temperature co-eflicient of resistance to be .0021.It has also been found that it has a hardness of 72, Brinnell scale,after cold-working and that while it is harder than very soft copper andsofter than cast iron, its ductility resembles that of copper or gold.The metal is relatively non-volatile up to its melting point.

Although we have described a preferred method of producing the morerefractory metals in the ductile form, it will be readily perceived fromthe various modifications described. and thereby be understood, that theinvention is of broad scope and we do not wish to be limited other thanby the spirit of the invention and the scope of the appended claims.

In some of the appended claims We have used the term more refractorymetals by which we mean such metals as uranium, thorium, zirconium,titanium, vanadium, chromium, and certain of the rare metal earths: thatis, such metals having oxides not reducible by hydrogen.

\Vhat is claimed is:

1. The method of forming coherent, rare refractory metals, the oxides ofwhich are not completely reducible by hydrogen, from a decomposablecompound, thereof, which comprises heating such a decomposable compoundto the decomposition temperature, removing the products of thedecomposition except the metal and continuing the heat treatment abovethe decomposition temperature until all of the metal is in a coherent,homogeneous form, said operations being conducted under non-oxidizingconditions and without exposure ofthe metal between said heat treatmentsto oxidizing conditions.

2. The method of forming coherent, rare refractory metals, the oxides ofwhich are not completely reducible by hydrogen, from a decomposablecompound thereof, which comprises heating such a decomposable compoundtothe decomposition temperature, removing the products of thedecomposition except the metal and continuing the heat treatment abovethe decomposition temperature until all of the metal is in a coherent,homogeneous form, said operations being conducted in an inertenvironment and without exposure of the metal between saidheattreatments to oxidizing conditions.

3. The method of forming coherent, rare refractory metals, the oxides ofwhich are not completelyreducible by hydrogen, from a decomposablecompound thereof, which comprises heating such a decomposable compoundto the decomposition temperature, removing the products of thedecomposition except the metal and continuing the heat treatment abovethe decomposition temperature until all of the metal is in a coherent,homogeneous form, said operations being conducted in a high vacuum andwithout exposure of the metal between said heat treatments to oxidizingconditions.

4. The method of forming coherent, homogeneous thorium which comprisesheating thorium hydride until the same is dissociated, removing thehydrogen and heating the thorium until it is in a coherent,

out exposure of the metal between said heattreatments to oxidizingconditions.

5. The method of forming coherent, homogeneous thorium which comprisesheating thorium hydride until the same is dissociated, removing thehydrogen and heating the thorium until it is in a coherent, homogeneousstate, said operations being conducted in a high vacuum and withoutexposure of the metal between said heat treatments to oxidizingconditions.

6. The method of forming coherent, homogeneous thorium from adissociable compound thereof which comprises heating a dissociablecompound of thorium until the same. is dissociated into thorium andgaseous products, removing the gaseous products and heating the thoriumuntil it is in a coherent, homogeneous state, said operations beingconducted under non-oxidizing conditions and without exposure of thethorium between said heat treatments to oxidizing conditions.

7. The method of forming coherent, homogeneous rare refractory metals,the 0X- ides of which are not completely reducible by hydrogen, frompowders thereof which comprises heating the powder of such a metal atsuch a temperature and rate that the gases are liberated withoutcombining with the metal or disintegrating the same, and continuing theheat treatment at a more elevated temperature until the metal is in acoherent, homogeneous state, said heat treatments being conducted undernon-oxidizing conditions and without exposure of the metal between saidheat treatments to oxidizing conditions.

8. The method of forming coherent, homo geneous rare refractory metals,the oxides of which are not completely reducible by hydrogen, frompowders thereof which comprises heating the powder of such a metal atsuch a temperature and rate that the gases are liberated withoutcombining with the metal or disintegrating the same, and continuing theheat treatment at a more elevated temperature until the metal is in acoherent, homogeneous state, said heat treatments being conducted in aninert environ-' ment and without exposure of the metal between said heattreatments to oxidizing conditions.

9. The method of forming coherent, homogeneous rare refactory metals,the oxides of which are not completely reducible by hydrogen, frompowders thereof which comprises heating the powder of such a metal atsuch a temperature and rate that the gases are liberated withoutcombining with the metal or disintegrating the same, and continuing theheat treatment at a more elevated temperature until the metal is in acoherent, homogeneous state, said heat treatments being conducted in ahigh vacuum and without exposure of the metal between said heattreatments to oxidizing conditions.

10. The method of forming coherent, homogeneous thorium from a powderthereof which comprises heating thorium powder at such a temperature andrate that all absorbed and adsorbed gases are substantially liberated,removing the liberated gases and continuing the heat treatment at a moreelevated temperature until the particles coalesce to form a coherent,homogeneous body, said heat treatments being conducted undernon-oxidizing conditions and without exposure of the thorium between theheat treatments to oxidizing conditions.

11. The method of forming coherent, homogeneous thorium from a powderthereof which comprises heating thorium powder at such a temperature andrate that all absorbed and adsorbed gases are substantilly liberated,removing the liberted gases and continuing the heat treatment at a moreele vated temperature until the particles coalesce to form a coherent,homogeneous body, said heat treatments being conducted in an inertenvironment and without exposure of the thorium between the heattreatments to oxidizing conditions.

12. The method of forming coherent, homogeneous thorium from a powderthereof which comprises heating thorium powder at such a temperature andrate that all absorbed and adsorbed gases are substantilly iiberted,removing the liberted gases and continuing the heat treatment at a moreelevated temperature until the particles coalesce to form a coherent,homogeneous body, saidheat treatments being conducted in a high vacuumand without exposure of the thorium between the heat treatments tooxidizing conditions.

13. The method of forming coherent, homogeneous thorium which comprisesslowly heating the thorium in the powder state to a temperature at whichthe particles coalesce, the rate of heat treatment being such that thethorium is denuded of absorbed and adsorbed gases prior to its reachinga temperature at which a combination of the gases and metal would takeplace, said heat treatment being conducted without exposure of the metalto oxidizing conditions.

14. The method of forming a coherent, rare refractory metal alloy, theoxides of the constituent metals of which are not completely reducibleby hydrogen, which comprises slowly heating a mixture of such metals inthe powder state to a temperature at which the particles thereofcoalesce, the rate of heat treatment being such that the material isdenuded of adsorbed and absorbed gases prior to its reaching atemperature at which a combination of the gases and metals would takeplace, said heat treatment being conducted without exposure of themetals to oxidizing conditions.

15. The method of forming coherent, homogeneous rare refractory metals,the oxides of which are not completely reducible by hydrogen, whichcomprises compressing such a metal in the powder state into a compactmass, preheating the compacted mass at such a'temperature and rate toliberate the adsorbed and absorbed gases without contaminating themetal, removing the liberated gases and continuing the heat treatment atsuch a temperature as to cause the particles to coalesce and form acoherent, homogeneous body, said heat treatments being conducted in aninert environment and without exposure of the metal between the heattreatments to oxidizing conditions.

16. The method of forming coherent, homogeneous rare refractory metals,the oxides of which are not completely reducible by hydrogen, whichcomprises compressing such a metal in the powder state into a compactmass, preheating the compacted mass at such a temperature and rate toliberate the adsorbed and absorbed gases Without contaminating themetal, removing the liberated gases and continuing the heat treatment atsuch a temperature as to cause the particles to coalesce and form acoherent, homogeneous body, said heat treatments being conducted in ahigh vacuum and without exposure of the metal between the heattreatments to oxidizing conditions.

17. The method of forming coherent, homogeneous thorium which comprisesagglomerating thorium powder to form a compact mass, heating the mass atsuch a temperature and rate as to liberate the gases therefrom withoutcontaminating the metals and further heat treating the metal at a highertemperature until the particles coalesce to form a coherent, homogeneousbody, said heat treatments being conducted in an inert environment andwithout exposure of the metal between the heat treatments to oxidizingconditions.

18. The method of forming coherent, homogeneous thorium which comprisesagglomerating thorium powder to form a compact mass, heating the mass atsuch a temperature and rate as to liberate the gases therefrom withoutcontaminating the metal and further heat treating the metal at a highertemperature until the particles coalesce to form a coherent, homogeneousbody, said heat treatments being conducted in a high vacuum and withoutexposure of the metal between the heat treatments to oxidizingconditions.

19. The method of producing rare refractory metals, the oxides of whichare not entirely reducible by hydrogen, in ductile form which comprisesproducing such a metal in powder form in a pure state and free fromsubstances which deleteriously affect its ductility, heating the owderat such a temperature and rate to liberate the adsorbed and absorbedgases, removing the liberated gases and continuing the heat treatment ata more elevated temperature until the particles coalesce and form aduetile body, said heat treatment being conducted in an inertenvironment and without exposure of the metal between heat treatments tooxidizing conditions.

20; The method of producing rare refractory metals, the oxides of whichare not entirely reducible by hydrogen, in duetile form which comprisesproducing such a metal in powder form in a pure state and tree fromsubstances which deleteriously affect its ductility, heating the powderat such a temperature and rate as to liberate the adsorbed and absorbedgases, removing the liberated gases and continuing the heat treatment ata more elevated temperature until the particles coalesce and form aduetile body, said heat treatment being conducted in an inertenvironment and without exposure of the metal between heat treatments tooxidizing conditions.

21. The method of producing rare refractory metals, the oxides of whichare not entirely reducible by hydrogen, in duetile form which comprisesproducing such a metal in powder form in a pure state and free fromsubstances which deleteriously affect its ductility,-compressing thepowder to form a compact mass, heating the mass at such a temperatureand rate as to liberate the adsorbed and absorbed gases, removing theliberated gases and continuing the heat treatment at a more elevatedtemperature until the particles coalesce and form a duetile body, saidheat treatment being conducted in an inert environment and withoutexposure of the metal between heat treatments to oxidizing conditions.

22. The method of producing rare refractory metals, the oxides of whichare not entirely reducible by hydrogen, in ductile form which comprisesproducing such a metal in powder form in a pure state and free fromsubstances which deleteriously afl'ect its ductility, compressing thepowder to form a compact mass, heating the mass at such a temperatureand rate as to liberate the adsorbed and absorbed gases, removing theliberated gases and continuing the heat treatment at a more elevatedtemperature until the particles coalesce and form a ductile body, saidheat treatment being conducted in a high Vacuum and without exposure ofthe metal between heat treatments to oxidizing conditions.

23. The method of producing rare refractory metals, the oxides of whichare not completely reducible by hydrogen, in ductile orm which comprisesreducing a compound of such a metal under such conditions that a purepowder is obtained which is free from substances deleteriously affectingthe workability of the metal, compressing the powder to. form a compactmass, heating the mass at a temperature and rate at which adsorbed andabsorbed gases are liberated without contaminating the metal, removingthe gases thus liberated,

and heat treating the mass until the parthe mass at a temperature andrate at which adsorbed and absorbed gases are liberated withoutcontaminating the metal, removing the gases thus liberated, and heattreating the mass until the particles coalesce to form a ductile body,said heat treatments being performed in a high vacuum and withoutexposure of the metal between the heat treatments to oxidizingconditions.

25. The method of producing rare refractory metals, the oxides of whichare not completely reducible by hydrogen, in ductile form, whichcomprises reducinga compound containing the metal under such conditionsthat substantially all substances deleteriously affecting theworkability of the metal are removed and a metal powder obtained whichis coarse, compressing the coarse powder to form a compact mass, heattreating the mass at a temperature and rate that adsorbed and absorbedgases are liberated, removing the liberated gases and further heattreating at more elevated temperatures until the particles coalesce toform a ductile body, said heat treatmentsbeing performed in an inertenvironment and without exposure of the metal between the heattreatments to oxidizing conditions.

26. The method of forming thorium in ductile form which comprisesreducing a compound containing thorium under such conditions thatsubstantially all substances deleteriously affecting the workability ofthorium are removed and a metal powder is obtained which is coarse,compressing the coarse powder to form a compact mass, heat treating themass at a temperature and rate that absorbed and adsorbed gases areliberated, removing the liberated gases and further heat treating atmore elevated temperatures until the particles coalesce to form aductile body, said heat treatments being performed in an inertenvironment and without. exposure of the metal between the heattreatments to oxidizing conditions.

27. The method of improving the properties of ductile, rare refractorymetals, the oxides of which are not completely reducible by hydrogen,which comprises producing such a metal in the coherent, homogeneousstate, free from such substances as deleteriously all'ect theworkability of the metal and then working the metal under nonoxidizingconditions to the desired form by rolling, swaging or drawing.

28. The method of improving the properties of ductile thorium whichcomprises producing thorium metal in a coherent, homogeneous state andtree from such substances as deleteriously affect the workability of themetal, and then working the metal under non-oxidizing conditions todesired form by rolling. swaging, or drawing.

29. The method of improving the properties of ductile, rare refractorymetals, the oxides of which are not completely reducible by hydrogen,which comprises reducing a compound containing such a metal to the purepowdered state, sintering the powder in a high vacuum at such atemperature and rate as to obtain a coherent, homogeneous body, andsubjecting the product thus obtained to mechanical working by rolling,swaging or drawing, said sintering and working operations being doneunder such conditions that substantially all deleterious substancesatt'ecting the workability of the metal are eliminated.

30. The method of improving the propel ties of ductile thorium whichcomprises forming thorium powder of a grain size capable of beingagglomerated into a mass which may be handled without crumbling, saidpowder being free from impurities affecting the mechanical working ofthe metal, agglomerating the powder into a compact mass, degasitying themass at temperatures at which the metal does not combine with the gases,further heating the agglomerated mass until it becomes coherent andhomogeneous, and mechanically working the coherent body to the desiredform by rolling, swaging or drawing.

In testimony whereof, we have hereunto subscribed our names this 4th dayof June 1924.

J OHN WESLEY MARDEN. HARVEY CLAYTON RENTSCHLER.

